In the process control industry, many control valve applications, such as power generation or petroleum refining applications, result in process conditions that produce unacceptable levels of aerodynamic noise. For example, a generally acceptable level of aerodynamic noise is approximately 85 dBA measured 1 meter downstream and 1 meter off the pipeline containing the control valve. It is understood that Fluid Pressure Reduction Devices implemented as valve trim or as vent diffusers can substantially reduce the noise generated within various process applications. The physics and fluid dynamics of these fluid pressure reduction devices and the prediction of aerodynamic noise in applications of fluid pressure reduction devices have been fairly well understood in recent years.
Conventional solutions to control valve noise problems include fluid pressure reduction devices of a cylindrical shape that implement special internal fluid structures to stage the pressure drop (i.e. control the pressure drop in discrete transitions within the fluid pressure reduction device) and/or the segregate of the fluid pressure reduction device outlet flow into multiple, smaller flow streams to reduce aerodynamic noise. Further, it is understood that conventional fluid pressure reduction devices use two general passageway cross sections: circular and rectangular. These passageway cross sections were typically limited by prior manufacturing capabilities. Due to these historical manufacturing and prediction technologies, these passageway cross sections continue in present implementations. Specifically, fluid pressure reduction devices constructed from stacked discs or investment cast plates generally produce rectangular cross section flow passage shape while cylindrically formed components with subsequent traditional machining operations yield circular cross section flow passage shapes.
The purpose of these flow passages is to create noise reduction structures within the fluid pressure reduction devices to reduce the amount of energy in the flow stream that is converted to noise and/or shift the frequency of the generated noise to levels beyond the audible range. One such common strategy to reduce aerodynamic noise is to minimize the size of apertures or reduce the cross-sectional area of the passageways in the fluid pressure reduction devices to induce a peak frequency shift of the generated noise beyond the audible range. Thus, to improve the performance of a fluid pressure reduction device, manufacturers make the flow passages as small as practical. However, this noise reduction technique is disadvantageous because it can reduce the overall flow capacity of the control valve and makes the fluid pressure reduction device susceptible to plugging or flow impediment.